Method of making waterproof boots by slush-molding



A g. 3, 1965 s. H. BINGHAM, JR

METHOD OF MAKING WATERPROOF BOOTS BY SLUSH-MOLDING 2 Sheets-Sheet 1 Filed Jan. 23, 1962 INVENTOR. flj'yazw, 72"; a WW 0 2W Aug. 3, 1965 s. H. BINGHAM, JR

METHOD OF MAKING WATERPROOF BOOTS BY SLUSH-MOLDING 2 SheetsSheet 2 Filed Jan. 23, 1962 United States Patent METHOD OF MAKING WATERPRGOF BGGTS BY SLUSH-MQLDING George H. Bingham, J12, Westminster, Md, assignor to Cambridge Rubber Company, Taneytown, Md, a corporation of Maryland Filed Jan. 23, 1962, Ser. No. 168,099 6 Claims. (Cl. 264-250) This invention relates to waterproof footwear, in particular, to plastic footwear made by the slush-molding process, and more especially to boots having heavy soles and heels including those having downwardly projecting cleats at the forepart portion of the sole. 7

In the manufacture of such boots by the slush-molding process, the hollow metallic mold, which is employed for the purpose, must have cavities corresponding to the downwardly projecing heel and to any other downwardly or laterally projecting elements such, for example, as transversely extending cleats or foxing beads. If, in the use of such a mold, it be attempted to provide a heavy, that is to say, thick wear-resistant outer sole, that is to say, bottom structure, difficulty may arise in removing the completely fused boot from the mold because those portion of the bottom of the boot, which result from the cavities in the bottom of the mold resist removal from said cavities if the outer sole be of any substantial thickness or rigidity. This is especially true when the downward projections are undercut, as when the projections extend outwardly, relatively to the side wall of the boot. Thus, to facilitate the removal of the boot from the mold, it has heretofore been thought necessary to increase the front-to-rear width of the mold at the ankle portion so as to furnish more clearance space for the withdrawal of the fused boot. However, this results in the production of a boot of a clumsy external appearance and one which, when in use, is loose on the foot so as to cause chafing and even the accidental pulling off of the boot if walking in deep mud or snow.

Not only is it diflicult to remove the fused boot from the mold but it is also difiicult to prepare the mold in the first instance. Since these molds are usually made by electroplating a model or prototype boot and since the metal mold is inflexible, the only feasible way of removing the model, after the electroplating operation is complete, is in some way to destroy the model, for example by burning or cutting it in pieces, an operation which is slow and laborious.

The present invention has for objects the provision of a novel method of making boots of the above type by f the employment of a hollow metallic mold and by the slush-molding process, whereby it i possible to make a boot of the desired external appearance and dimensions and such as will have a proper fit to the wearers foot, but which may have as heavy and rigid an outer sole as desired, or one which is provided with downwardly directed cleats of any desired shape, or lateral projections. A further object is to provide a method of making such a boot whereby the foot-supporting inner surface of the boot may have any desired characteristics, while the outer or tread surface of the outer sole or bottom structure may have other characteristics, in particular, resistance to wear. A further object is to provide a novel method of making a mold for use in the manufacture of such a boot whereby the difiiculties commonly experienced in the removal of the model are substantially avoided.

Other and further objects and advantages of the invention will be pointed out in the following more detailed description and by reference to the accompanying drawings wherein:

FIG. 1 is a side elevation of a boot such as may be made in accordance with the herein described method;

3,198,864 Patented Aug. 3, 1965 'ice FIG. 2 is a fragmentary, diagrammatic, transverse section through the heel of the boot on the plane of the line 2-2 of FIG. 1;

FIG. 3 is a similar vertical, transverse section on the line 3-3 of FIG. 1;

FIG. 4 is a diagrammatic side elevation illustrative of a boot having certain undesirable characteristics such as result from the practice of prior processes for the manufacture of thick-soled boots by the slush-molding method;

FIG. 5 is a diagrammatic, vertical, front-to-rear section through a mold useful in the practice of the present method;

FIG. 6 is a transverse section through the mold shown in FIG. 5, illustrating certain steps in the method of making a boot such :as that of FIG. 1, in accordance with the present invention;

FIG. 7 is a bottom view of a midsole such as may be employed in the practice of the present method;

FIG. 8 is a section to larger scale of the line 88 of FIG. 7; and

FIG. 9 is a front-to-rear diagrammatic vertical section showing a boot such as results from the practice of the present invention.

Referring to FIGS. ,1 to 3 of the drawings, the character B indicates a boot of the type to which the present invention relates, this boot having the high leg portion 20,

the downwardly projecting heel 21 and the thick, heavy outer sole or bottom 22, the latter being shown as having downwardly directed, transversely extending cleats 23 and/or a laterally projecting rib 23m at its upper edge. In FIG. 2 the leg of this boot of FIG. 1 is shown as consisting of or comprising an exterior layer 21 which also 7 forms the outer ply of the heel 21. In the heel this layer 21 houses a mass 21a of appropriate material to form a solid core. The forepart portion of the sole also comprises the exterior layer 21, which, at the region of the cleats 23, is shaped to provide cavities for the reception of core material 23a. The numeral 24 in FIGS. 2 and 3, indicates the upper surface, that is to say, the footsupporn'ng inner surface of the boot which,was shown in these figures, is substantially flat and horizontal. However, in accordance with the invention, this upper surface 24 of the boot bottom may be of any desired shape, either transversely or from front-to-rear. As will be noted, this boot, at the ankle region, indicated by the line 'X-Y is relatively narrow from front-t-o-rear, a compared with the leg above the ankle so as to insure a good fit.

Assuming that there has been provided a mold M (FIG. 5), such as would ordinarily be employed for the slush-molding of a boot having an exterior surface like that of FIG. 1, that is to say, having cavities H, C and D in its interior corresponding to the shapes of the outer surfaces of the heel, cleats and peripheral rib, the procedure in manufacturing a. boot, in accordance with the present invention, would comprise as its first step, as illustrated in FIG. 6, the filling of the mold M with a plas FIG. 5. If at this time, the still fluid plastic be poured out of the mold and the mold be further heated so as to fuse the plastic layer P, the resultant flexible thin-walled boot may be removed without too much difiiculty from the mold. However, such a boot would be impractical for use by persons requiring a boot having a heavy, moreor-less rigid, and wear-resistant outer sole or bottom. On the other hand, if the fluid plastic forming the layer P were permitted to remain in the mold, while applying more heat to the bottom of the mold than to the leg portion, so as to provide a thick sole or bottom portion, before pouring out the surplus plastic, and then fused, the resultant heavy bottom would be so rigid that it would be ditlicult, or even impossible, to withdraw the boot from a mold such as that of FIG. 6 designed to provide a boot shaped to fit the wearer across the ankle portion, that is to say, at the plane of the line X-Y (FIG. 6).

In accordance with the present invention, after the ply P of plastic has been gelled within the mold M, this ply is then cured just sufiiciently to permit it to be withdrawn from the mold asa unitary embryo or skeleton boot. After this embryo boot has been withdrawn from the mold, then the desired thickness of outer sole or bottom structure may be provided, either by introducing fluid plastic into this embryo boot, so as to form a bottom of the desired thickness, while filling the cavities corresponding to the shapes of the outer surfaces of the cleats and peripheral rib, and then subjecting the boot to heat sufficient to fuse this fluid plastic, or by the use of a self-curing plastic to avoid the necessity for such heating.

As an alternative, a suitable midsole may be prepared and introduced as a unit into the embryo boot and secured in place, for example by a suitable adhesive, such as a self-curing plastic. Such a midsole is diagrammatically illustrated in FIGS. 7 and 8. This midsole may be prepared from plastic in a simple cup-type mold, shaped to provide the heel core 210:, the cleat cores 23a, and peripheral rib core-desirably integral with the midsole proper indicated at 25. Such a midsole may be made of any suitable material, for example of fused plastic and, while it may be of the same material throughout, it is readily possible, in accordance with this procedure, to make certain parts of one material and others of some other material. For instance, the heel and cleat cores may be of sponge plastic while the upper, main portion of the midsole may be of a plastic like that which forms the outer wall of the boot, or it may, for example, be of heat-insulating character such, for instance, as a plastic having uniformly distributed therein discrete particles of low heat conductivity. Alternatively, if desired, the lower portion of this midsole may be made of a hard unyielding material while the upper layer may be of a softer more resilient material, for instance a sponge plastic, or it may be a textile fabric or thin leather adhesively bonded to a rigid lower portion.

Assuming that such a midsole has been prepared, the unclersurface of this midsole may be coated with a suitable adhesive, assuming that the rnidsole has been fully cured, and then fitted into the embryo boot S (FIG. 9) and pressed into place, so that the projecting portions of the insole will fit into the cavities in the interior surface of the embryo boot.

On the other hand, assuming that the embryo boot S has not been fully cured and that the midsole I is not completely fused, the midsole may be introduced into the embryo boot and then the assembly subjected to heat, for example to the heat of infrared lamps so as concomitantly to complete the curing of these parts and their integral bonding together.

A boot so made, while having any desired thickness and rigidity of outer sole or bottom with any selected external pattern, including a heavy, downwardly projecting heel and cleats, may in accordance with the present invention be of the form-fitting shape desired, that is to say, having a narrow ankle portion, as illustrated in FIG. 6, so that, when worn, the boot closely hugs the wearers foot and leg and does not cause chafing nor tend to pull loose when walking in adhesive material. This is in marked contrast with customary boots made by slushmolding and having cleated slots, as illustrated in FIG. 4, wherein the ankle dimension M-N is large and the boot is loose and of clumsy appearance.

As above noted, the preparation of a mold such as that of FIG. 5, in accordance with usual methods, involves difliculties, in particular, that of removing the model from the rigid mold formed by electroplating the model.

The present invention solves the above difiiculty by first providing a model having a bottom or tread surface which is substantially smooth. Then blocks of material, corresponding in shape to the external projections of the boot to be manufactured, for example, a heel and cleats or other projecting elements, are made from a softly resilient material, such, for example, as sponge plastic, and adhesively bonded to the smooth outer surface of the model. When such a model or prototype is electroplated, the yielding character of the downward projections is such as to make it readily possible to pull the model from out of the metal shell, even though it be of form-fitting design, without requiring that the model be destroyed.

While certain embodiments of the present invention have herein been illustrated by way of example and described in detail, it is to be understood that the invention is broadly inclusive of any and all modifications, both of apparatus, materials employed and process steps, constituting equivalents of the method steps, materials and apparatus of the appended claims.

I claim:

1. That method of making, by the slush-molding process, a waterproof, snug-fitting boot having a bottom structure which is thicker and less flexible than the upper and which has a solid heel at its rear end and downward projections at its forepart portion, said method comprising as steps: providing a hollow one-piece metallic mold whose inner surface contour is a replica, but in reverse, of the outer surface of the boot to be made, employing said mold, according to conventional slush-molding procedure, in preparing an embryo boot of the desired external contour but whose bottom structure is of substantially the same thickness and flexibility as its upper, and wherein the heel and said projections are hollow, fusing this embryo boot just sufiiciently to permit it to be withdrawn as a unit from the mold, withdrawing the embryo boot from the mold and so introducing material into the embryo boot as to fill the cavities in its bottom structure and to build up an outer sole or bottom of the desired character, and so treating the resultant assembly as permanently to bond the material of the embryo boot with the material which was so introduced while completing the fusing of the embryo boot.

2. That method of making, by the slush-molding process, a waterproof, snug-fitting boot having a bottom structure which is thicker and less flexible than the upper and which has a solid heel at its rear end and downward projections at its forcpart portion, said method comprising as steps: providing a hollow one-piece metallic mold whose inner surface contour is a replica, but in reverse, of the outer surface of the boot to be made, employing said mold, according to conventional slush-molding procedure, in preparing an embryo boot of the desired external contour but whose bottom structure is of substantially the same thickness and flexibility as its upper, and wherein the heel and said projections are hollow, fusing this embryo boot just sufiiciently to permit it to be withdrawn as a unit from the mold, withdrawing the embryo boot thus formed from the mold, and providing a midsole whose bottom surface is of a contour like that of the bottom of the embryo boot, but in reverse, introducing this midsole into the embryo boot and so placing it that it fits snugly within and against the bottom of the embryo boot, and bonding the midsole to the bottom of the embryo boot.

3. The method according to claim 2, wherein the midsole is of semicured plastic and, after its introduction into the embryo boot, the assembly is subjected to heat such as to complete the curing of the midsole and concomitantly integrally bond it to the inner surface of the bottom of the embryo boot.

4. The method according to claim 1, wherein the material introduced into the embryo boot is in fluid condition and is caused to form a gelled layer within the bottom of the embryo boot filling the cavities in the latter and which is of sufficient thickness to provide an outer sole or bottom of the desired thickness and rigidity, and then subjecting the assembly to heat such as to complete the fusing of the embryo boot and of the material introduced therein and concomitantly to bond said materials to form an integral bottom structure.

5. The method according to claim 4, wherein at least a portion of the material, which is introduced into the boot, in fluid form, contains a blowing agentwhereby, during the curing operation, such material is blown to form a sponge structure.

6. The method according to claim 1, wherein the material which is introduced into the embryo boot in fluid condition is a plastic of a type such that, when it is cured, it becomes more hard, tough and wear-resistant than the material which forms the upper of the boot.

References Cited by the Examiner UNITED STATES PATENTS 7/ Sedgwick et a1. 204-14 1/ 26 Bart 20414 12/ 31 Howarth 3 67.3 1/ 39 Richards 3 6'-7 .3 9/49 Auzin l56242 1/51 Jenett 15 6242 1/57 Kish 264250 4/ 59 Wibbens 264-,255 6/ 60 Hickler 18-5 8 5/62 Bingham 264--255 10/62 Schilling 264250 FOREIGN PATENTS 5/58 Canada. 4/61 Canada.

ROBERT F. WHITE, Primary Examiner.

WILLIAM J. STEPHENSON, ALEXANDER H.

BRODMERKEL, Examiners. 

1. THAT METHOD OF MAKING, BY THE SLUSH-MOLDING PROCESS, A WATERPROFF, SNUG-FITTING BOOT HAVING A BOTTOM STRUCTURE WHICH IS THICKER AND LESS FLEXIBLE THAN THE UPPER AND WHICH HAS A SOLID HEEL AT ITS REAR END AND DOWNWARD PROJECTIONS AT ITS FOREPART PORTION, SAID METHOD COMPRISING AS STEPS: PROVIDING A HOLLOW ONE-PIECE METALLIC MOLD WHOSE INNER SURFACE ONTOUR IS A REPLICA, BUT IN REVERSE, OF THE OUTER SURFACE OF THE BOOT TO BE MADE, EMPLOYING SAID MOLD, ACCORDING TO CONVENTIONAL SLUSH-MOLDING PROCEDURE, IN PREPARING AN EMBRYO BOOT OF THE DESIRED EXTERNAL CONTOUR BUT WHOSE BOTTOM STURCTURE IS OF SUBSTANTIALLY THE SAME THICKNESS AND FLEXIBILITY AS ITS UPPER, AND WHEREIN THE HEALL AND SAID PROJECTIONS ARE HOLLOW, FUSING THIS EMBRYO BOOT JUST SUFFICIENTLY TO PERMIT IT TO BE WITHDRAWN AS A UNIT FROM THE MOLD, WITHDRAWING THE EMBRYO BOOT FROM THE MOLD AND SO INTRODUCING MATERIAL INTO THE EMBRYO BOOT AS TO FILL THE CAVITIES IN ITS BOTTOM STRUCTURE AND TO BUILD UP AN OUTER SOLE OR BOTTOM OF THE DESIRED CHARACTER, AND SO TREATING THE RESULTANT ASSEMBLY AS PERMANENTLY TO BOND THE MATERIAL OF THE EMBRYO BOOT WITH THE MATERIAL WHICH WAS SO INTRODUCED WHILE COMPLETING THE FUSING OF THE EMBRYO BOOT. 